The Permian–Triassic (P–Tr) extinction event, colloquially known as the Great Dying, the End Permian or the Great Permian Extinction, occurred about 252 Ma (million years) ago, forming the boundary between the Permian and Triassic geologic periods, as well as the Paleozoic and Mesozoic eras. It is the Earth's most severe known extinction event, with up to 96% of all marine species and 70% of terrestrial vertebrate species becoming extinct. It is the only known mass extinction of insects. Some 57% of all families and 83% of all genera became extinct. Because so much biodiversity was lost, the recovery of life on Earth took significantly longer than after any other extinction event, possibly up to 10 million years.
There is evidence for between one and three distinct pulses, or phases, of extinction. Suggested mechanisms for the latter include one or more large bolide impact events, massive vulcanism, coal or gas fires and explosions from the Siberian Traps, and a runaway greenhouse effect triggered by sudden release of methane from the sea floor due to methane clathrate dissociation or methane-producing microbes known as methanogens; possible contributing gradual changes include sea-level change, increasing anoxia, increasing aridity, and a shift in ocean circulation driven by climate change.